This disclosure relates to the perforation of a well casing. It was designed specifically for use on water wells, but can be used in conjunction with steel casings on any type of well structure.
The need for perforating a well casing is well known in the drilling industries. By perforating a casing at various depths corresponding to the strata in which liquid is located, one can combine the flow from several different layers to achieve the production requirements of a particular well.
Various types of devices have been previously proposed for perforating well casings. Laterally movable punches are exemplified by the devices shown in the U.S. Pat. Nos. to Jobe, 2,482,913, Frogge, 3,212,580 and Grable, 3,720,262. These involve the application of substantial pressures necessary to push a punch radially through a well casing and to subsequently retrieve the punch for tool removal.
A fluid jet perforator is illustrated in U.S. Pat. No. 3,266,571. Explosive perforators are used widely in oil drilling operations. However, the cost of these devices is such as to make them prohibitive in the drilling of a conventional water well.
A number of patents granted in the period from 1915 to 1924 utilized the rolling engagement of a toothed wheel to perforate the casing of a well. These patents are as follows: Graham, U.S. Pat. No. 1,162,601; Noble, U.S. Pat. No. 1,247,140; Baash, U.S. Pat. No. 1,259,340; Baash, U.S. Pat. No. 1,272,597; Layne, U.S. Pat. No. 1,497,919; Layne, U.S. Pat. No. 1,500,829; and Layne, U.S. Pat. No. 1,532,592.
Most of these patents illustrating a toothed wheel perforating tool utilize inclined slots or guides to cam the wheel radially outward as the perforating tool is moved downwardly in a well casing by mechanical force. They do not provide positive control of the wheel placement for accurate elevational positioning of the resulting perforations. The last two patents to Layne disclose a perforating wheel mounted on a pivoted arm. The arm is wedged radially outward by a mechanical pin controlled by a cable which can be pulled at the working surface. The wheel pressure is directed onto the pin, which will therefore be wedged within the tool under substantial forces. Mechanical arrangements must be provided to accommodate possible breakage of the control cable.
While these patents showing perforation by a rotatable wheel illustrate projected developments more than fifty years old, such perforating tools are not generally available on the market today. The present device has been developed to provide a mechanically simple and effective means for assuring the application of the substantial radial pressures required to perforate steel well casings of the type conventionally used for water wells. The present tool is designed specifically for use in conjunction with conventional pneumatic drilling equipment. No extraneous triggering devices, cables or mechanical interlocks are required. It utilizes the pneumatic pressure conventionally available within the drill rod to preset the wheel for rolling engagement with the wall of the well casing. Actual perforation is accomplished by rolling movement of the extended toothed wheel due to downward movement of the tool under the influence of the connected drill rod. Retraction of the wheel by reverse rolling movement is assured upon the reversal of the movement of the drill rod as the tool is pulled upwardly.